The present invention relates to a device for determining and/or controlling the operating data of automotive vehicles having an internal combustion engine, with at least one resistance voltage divider with variable division ratio as position transmitter.
The forward movement of automotive vehicles having an internal combustion engine is generally controlled, in accordance with the wishes of the driver, by a setting device, in particular an accelerator pedal, the instantaneous position of which is transmitted to an element which directly or indirectly meters the amount of fuel. This element which meters the amount of fuel can either be the throttle valve or the displacement lever of a fuel injection pump.
For various reasons it may be desirable to provide an electric connection between the setting device and the device feeding the fuel, instead of a mechanical connection. In particular, in the case of commercial vehicles with below-the-floor or rear engines and in the case of pivoted buses with rear engine, the necessary pedal forces can in the case of mechanical transmission by rods or Bowden cable only be kept low and independent of movements of the vehicle by careful placement.
In addition to this, such devices are of unfavorable construction from the standpoint of installation and maintenance.
Devices for maintaining the speed of automotive vehicles constant are also known in which there is no fixed association between the instantaneous position of the setting device and the throttle valve or displacement lever of the fuel injection pump.
It is already known, in a device for regulating the speed of travel of an automotive vehicle having a setting member which is adapted to be actuated by the driver, particularly a gas pedal, to develop the transmission to an element which controls the formation of the fuel/air mixture in such a manner that a follow-up control with a first position transmitter takes place at the desired value input of a controller and with a second position transmitter at the actual-value input thereof. In this connection, the first position transmitter is connected to the gas pedal and the second position transmitter to the throttle valve for the supplying of a return message, the throttle valve being adjusted by a servo-motor in order to adapt the actual-value to the desired value.
Since only the position transmitter is connected to the gas pedal, the pedal forces remain low and are not affected even by twists and movements of the vehicle body. The electric line connecting gas pedal and throttle valve or injection pump can be installed without difficulty or restrictive conditions.
For the forming of the electric signal which represents the desired-value and the production of the return-report signal, mechanically variable resistors (potentiometers) are generally provided as voltage dividers. Only relatively narrow tolerances are permitted for the electric values in view of the required precise association between voltage value and potentiometer position. These tolerances must be maintained even after lengthy periods of operation. However, as a result of aging and the action of fuel, oil, water of condensation and dust, they may develop side paths to the resistance paths, so-called leakage resistances, which falsify the original values and thus the association between signal voltage and wiper position. This can lead to undesired or even dangerous conditions of travel.
It is therefore known to provide reference switches which switch upon pre-determined positions of the wipers of the potentiometers. The signal voltage which was tapped off at that moment must lie within a narrow tolerance. Installation and adjustment of the reference switches is time-consuming and expensive.